The invention relates to a hydraulic steering unit comprising a housing having a pressure chamber which has an aperture at one end through which a rotatably mounted steering control apparatus is led to the outside and the aperture is sealed from the outside by a sealing ring.
Such a steering unit is marketed by the applicants under the name "OSP". Such steering units are used in "downstream" operations, i.e. the steering unit is disposed in series between a pump and further downstream hydraulic equipment. In the pressure chamber, there is hydraulic fluid which is under a certain pressure, namely the supply pressure of the downstream hydraulic equipment. By means of the steering control unit, for example a slide connected to a steering column, various control orifices are freed or closed to let the hydraulic fluid reach hydraulic motors which finally turn the wheels. When the pressure in the pressure chamber rises, the sealing ring is more intensely loaded. The friction between the steering control apparatus and the sealing ring is increased. The wear on the sealing ring brought about by movement of the steering control apparatus, i.e. by rotation of the steering column, is increased. In addition, operation of the steering control apparatus is made more difficult by the higher frictional torque.
It is the problem of the present invention to provide a steering unit which is simple to assemble and has a longer life.
This problem is solved in a steering unit of the aforementioned kind in that between the sealing ring and pressure chamber there is a one-piece pressure reduction ring which surrounds the steering control apparatus, that between the pressure reduction ring and sealing ring there is a fluid collecting chamber with an outlet, and that the pressure reduction ring comprises a circumferential flange-like projection which lies sealingly against the end of the pressure chamber.
From U.S. Pat. No. 3,044,785, it is known in an axially movable piston rod to relieve a sealing ring by providing a metal bushing around the piston rod between the pressure chamber and the sealing ring, the hydraulic fluid being able to flow past the bushing. Between the metal bushing and the sealing ring, provision is made for the hydraulic fluid to flow out. The metal bushing is made of relatively many parts. Assembly is difficult. Moreover, the known seal takes up relatively much space.